What do I need to become a Blender developer?
Great question! There are many ways to help developing Blender. The best way is to find things to improve first, like fixing bugs. That'll help getting familiar with the code and structure of Blender. The first place to start is the wiki page https://wiki.blender.org/index.php/Dev:Contents, mostly the "Getting Started" section.

Also drop by on IRC, channel #blendercoders on Freenode. There you'll find friendly developers you can ask all kind of questions.